Ferrous complex of n-containing heterocyclic compound as silver latent image stabilizer

ABSTRACT

Photographic material comprising at least one silver halide emulsion layer, which is improved with respect to the stability of the latent image and the final silver image by addition of a complex compound of iron with a nitrogen-containing heterocyclic compound having a five- or six-membered heterocyclic ring as ligand.

United States Patent Matejec et al.

[ Feb. 1, 1972 [54] FERROUS COMPLEX OF N- CONTAINING HETEROCYCLIC COMPOUND AS SILVER LATENT IMAGE STABILIZER [72] lnventors: Reinhard Matejec; Rudolf Meyer, both of Leverkusen; Wollgang Himmelmann, Opladen-Luetzenkirchen, all of Germany [73] Assignee: Farbenfabriken Bayer Aktiengesellschaft,

Leverkusen, Germany [22] Filed: July 9, 1969 [21] Appl. No.: 840,533

[30] Foreign Application Priority Data July 19, 1968 Germany ..P 17 72 903.2

[56] References Cited UNITED STATES PATENTS 2,432,865 12/1947 Dimsdale et al. ..96/109 X 3,086,863 4/1963 Hunt et a]. ..96/109 X 3,312,552 4/1967 Bardorff et al ..96/109 X Primary Examiner-Norman G. Torchin Assistant ExaminerWon H. Louie, .lr. Attorney-Connolly and Hutz [57] ABSTRACT 2 Claims, No Drawings FERROUS COMPLEX OF N-CONTAINING HETEROCYCLIC COMPOUND AS SILVER LATENT IMAGE STABILIZER This invention relates to a light-sensitive photographic material with at least one light-sensitive silver salt emulsion layer with improved stability both for latent images and for visible silver images.

The most important binding agent for silverhalide emulsion layers is still gelatin, although there have been many attempts to replace gelatin by synthetic binding agents. One disadvantage of gelatin, since it is a natural product, is that it is not possible to guarantee any degree of reproducibility in its production. Different samples of gelatin have properties that differ in dependence upon the starting materials and processes used in their production, and it is only possible to obtain a starting material for the production of photographic layers with fairly uniform properties by blending different samples of gelatin. Contrary thereto synthetic binding agents can be produced with much more uniform properties. 1t has, however, not yet been possible to produce synthetic binding agents whose photographic properties approach those of natural gelatin. The advantage of gelatin in this respect is that it increases the light-sensitivity of silver halides. This efiect is generally attributed to the presence of substances containing sulfur which, as ripening agents, increase the sensitivity of the silver halide compounds. In addition, gelatin is also above to a certain extent to stabilize metallic silver and latent silver images in particular, against the oxidizing effect of atmospheric oxygen.

In view of this very effect, gelatin is superior to other hydrophilic and in particular synthetic binding agent.

Accordingly, there is considerable interest in developing agents for gelatin and other binding agents which improve the stability of latent images.

It is among the object of the present invention to provide light-sensitive photographic layers having improved stability in respect either of the latent image or of the final silver image.

We now have found a photographic material with at least one supported silver halide emulsion layer, this layer containing a complex compound of iron with a nitrogen-containing heterocyclic compound having a five or six-membered heterocyclic ring as ligand.

lron complexes of bivalent iron are preferred, although complexes of trivalent iron may also be used. Whenthese complexes are used in silver halide gelatin emulsions, and Fe /Fe -ratio which corresponds to the Redox potential of the emulsion for a given normal potential of the particular iron complex used, is in any case adjusted.

The stabilizing effect of the iron complexes is presumably based upon their catalyze activity, i.e., on a protective effect against oxidation by atmospheric oxygen. The stabilizing effect is on the latent image specks.

The effect of the iron complexes was particularly surprising because inorganic iron salts, for example iron (ID-sulfate, actually intensify the bleaching out of silver images and in particular the destruction of latent images, i.e., so-called fading," which is a considerable disadvantage.

In a preferred embodiment of the invention, the complex compounds are used with an excess of nitrogen-containing heterocyclic compounds, preferably in a molar ratio of from about 4 to 6 mols of the heterocyclic compound per mol of iron ions. The heterocyclic compounds themselves show hardly any activity at all in the absence of iron ions.

The following heterocyclic compounds, for example, are suitable ligands for the iron complex used in accordance with the invention: compounds of the pyrrole, pyrroline or pyrrolidine series; compounds of the imidazole, imidazoline or imidazolidine series such as benzimidazole or naphthimidazole, pyridine and derivatives or hydrogenation products thereof; quinoline or indole and derivatives thereof; compounds of the oxazole series such as benzoxazole, benzoxazinc or pyrazole, pyrazoline or pyrazolidine or their derivatives.

Particular utility is exhibited by the following heterocyclic compounds: N-methylpyrrole, benzimidazole, imidazole, 2- methylimidazole, ethylene urea (2-imidazolidone), poly-2- vinyl pyridine, poly-5-methyl-2-vinyl pyridine, tetrahydroquinoline, 2-methyl benzoxazole, 3-hydroxy indole, 2,4- dihydroxy quinoline, pyrrolidone, 3methyl-5-pyrazolone, 2- benzoxazolinone and 2,3-dihydro-l ,4-benz-3 oxazinone.

The aforementioned heterocyclic compounds may contain any substituents, for example alkyl or alkoxy with preferably up to five carbon atoms which may be substituted by hydroxyl, halogen such as chlorin or bromin, carboxyl, sulfo, phenyl etc.

The type of heterocyclic compounds used is not, in principle, important. They only should be photographically inactive in that the heterocyclic compounds have no deleterious effect on the photographic properties of the emulsion, i.e., mercaptoor thio-substituted rings cannot be used as ligands in these compounds because such substituted rings show no catalyze activity. Preferred are water-soluble and uncolored or only slightly colored complex compounds with the iron ions.

The iron complexes may be added to the photographic emulsion at any stage during its preparation, preferably after chemical ripening. The required effect is also obtained when a final silver halide emulsion layer is washed in an aqueous solution of the iron complex. Alternatively, the required quantity of the iron complex may also be added to the binding agents before the photographic layer is actually prepared.

The quantity in which the iron complexes are added may vary within wide limits, being governed by the effect required and also by the type of emulsion used. The optimum quantity in any one instance may readily be detem'lined by a few simple tests. In general, quantities of from 0.5 mg. to 5 g. of iron, in the form of the complex, per liter of silver halide emulsion have proved to be adequate. The molar ratio of iron to the heterocyclic ligand is from 1:2 to 1:10 and preferably from 1:4 to 1:6 as mentioned above. The effect according to the invention is fully obtained when simple solutions of iron salts,

preferably salts of iron (II) and the water-soluble heterocyclic compounds, in the molar ratio specified above, are added to the silver halide emulsion. The iron complex compound does not have to be isolated before it is used.

The effect of the iron complex is apparent not only in gelatin-containing silver halide emulsion layers, but also with particular intensity in emulsion layers of the kind in which all or part of the gelatinhas been replaced by other natural or synthetic hydrophilic binding agents. Examples of binders such as these include other proteins, such as casein or albumin; starch or starch derivatives, such as starch ethers or starch esters; cellulose or derivatives thereof such as carboxyalkyl cellulose, in particularcarboxymethyl cellulose, or alkylated cellulose such as hydroxy-ethyl cellulose; alginic acid and derivatives thereof, for example alkali metal salts of alginic acid, in particular sodium alginate, or alginic acid esters; and synthetic binders such as polyvinyl pyrrolidone, polyvinyl alcohol or partly hydrolized polyvinyl acetate. In addition, the latent image is also stabilized in layers of the kind containing colloidal silica as binder.

The iron complexes may be used in any silver halide emulsions. Silver chloride, silver bromide or mixtures thereof, which may contain silver iodide up to 10 mol percent, may be used as the silver halide.

The emulsions may also contain chemical sensitizers, for example, reducing agents such as stannous salts; polyamines such as diethylene triamine; and sulfur compounds of the type described in U.S. Pat. No. 1,574,944. The emulsions in question may also be chemically sensitized by salts of noble metals, such as ruthenium, rhodium, palladium, iridium, platinum or gold as described in the paper by R. Koslowsky, in Z.Wiss.Phot., 46, 65-72 (1951).

The emulsions may also contain polyalkylene oxides, in particular polyethylene oxide and derivatives thereof, as chemical sensitizers.

The emulsions according to the invention may contain the conventional stabilizers, for example: homopolar or saltlike compounds of mercury with aromatic or heterocyclic rings, such as mercapto triazoles, single mercury salts, sulfoniummercury double salts and other compounds of mercury. Azaindenes, preferably tetraor pentaazaindenes, in particular those of the kind substituted by hydroxyl or amino groups, are also suitable for use as stabilizers. Compounds of this kind are described in the paper by Birr in Z.Wiss.Phot., 47, 2-58 1952) other suitable stabilizers include inter alia heterocyclie mercapto tetrazole, quaternary benztriazole derivatives and benztriazole.

The emulsions may be hardened in the conventional way, for example with fonnaldehyde or halogen-substituted al dehydes containing a carboxyl group, such as mucobromic acid, diketones, methane sulfonic acid esters and dialdehydes.

EXAMPLE 1 One hundred ml. of a 0.5 N silver nitrate solution and 100 ml. of a 0.55 -N potassium bromide solution are simultaneously added while stirring to 100 ml. of a 2.5 percent by weight aqueous solution of polyvinyl alcohol.

The solution is then ripened with the precipitated AgBr for IS minutes at 40 C. Ten mg. of l-phenyl-S-mercaptotctrazole per liter are then-added to the emulsion. The additivcs listed below are then added to the casting solution.

The layers are exposed behind a grey wedge and, after expo sure, are stored in a heating chamber for different periods at 60 C./40 percent air humidity. After storage, they are developed in a developer of the following compositions p-methylaminophenol l g.

sodium-sulfite (anhydrous) 13 g. hydroquinone 3 g. sodium carbonate 26 g.

l liter of water.

The various test samples contained the following additives:

Sample l: 25 ml. of a 0.1 percent by weight solution of commercial catalyze.

Sample 2: 25 ml. of a 0.3 percent by weight aqueous solution of ferrous sulfate per liter of emulsion.

Sample 3: 25 ml. per liter of emulsion of a solution containing per 100 cc., 0.3 g. of iron sulfate and 0.6 g. of N- methylpyrrole.

Sample 4: 25 ml. per liter of emulsion of a solution containing per 100 cc., 0.3 g. of iron sulfate and 0.6 g. of benzimidazole.

Sample 5: 25 ml. per liter of emulsion of a solution containing, per 100 cc., 0.3 g. of iron sulfate and 0.6 g. of imidazole.

Sample 6: 25 ml. per liter of emulsion of a solution containing, per I cc., 0.3 g. of iron sulfate and 0.6 g. of 2- mcthylimidazole.

The stabilizing effect of the iron complexes is shown in the following table:

TABLE 1 Sensitivity in Number of xvi wedge Steps Development Immediately Development 8 days Fifty ml. of a 0.7 N silver nitrate solution and 50 ml. of a 0.75 N potassium bromide solution are simultaneously added with stirring over aperiod of minutesat 40 C to ml. of

an 8 percent by weight aqueous solution and 20 ml. of a 1.5

percent by weight aqueous solution of ethanolamine alginate.

The resulting photographic emulsion is hardened, shredded,

washed with water and then further treated as described in example l. The following additives were introduced into the individual test samples before casting:

l: 25 ml. of a 0.1 percent by weight solution of commercial catalyze.

2: 25 ml. of a 0.3 percent by weight aqueous solution of ferrous sulfate per liter of emulsion.

3: 25 ml. of a 0.6 percent by weight aqueous solution of N- methyl pyrrole.

4: 25 ml. of a 0.6 percent by weight aqueous solution of benzimidazole.

5: 25 ml. per liter of emulsion of a solution containing, per

cc., 0.3 g. of iron sulfate and 0.6 g. of N-methyl pyrrole.

6: 25 ml. per liter of emulsion of a solution containing, per

100 cc., 0.3 g. ofiron sulfate and 0.6 g. of benzimidazole.

7: 25 ml. per liter of emulsion of a solution containing, per

100 cc., 0.3 g. ofiron sulfate and 0.6 g. ofimidazole.

: 25 ml. per liter of emulsion of a solution containing, per 100 cc., 0.3 g. of iron sulfate and 0.6 g. of 2-methyl imidazole.

9: 25 ml. per liter of emulsion of a solution containing, per 100 cc., 0.3 g. of iron sulfate and 0.6 g. of ethylene urea.

I0: 25 ml. per liter of emulsion ofa solution containing, per lOO cc., 0.3 g. of iron sulfate and 0.6 g. of polyvinyl pyridine.

ll: 25 ml. per liter of emulsion of a solution containing, per

100 cc., 0.3 g. ofiron sulfate and 0.6 g. of poly-S-methyl- 2-vinylpyridine.

The stabilizing effect on the emulsion are shown in the following table:

TABLE 2 Sensitivity in Number of Z-Wodgc Steps Development Immediately Development 8 Days Test After Exposure After Exposure Comparison, no additives Standard 4 1 +2 +1 2 -3 -6 3 +1 -.-3 4 0 Z 5 +5 +l 6 +3 +1 7 +5 +1 8 7 +3 9 +3 +l l0 +4 +2 I l +3 +l What is claimed is:

l. A light-sensitive photographic material containing at least one supported silver halide emulsion layer which emulsion layer contains in an amount of 0.5 mg. to 5 g. per liter of emulsion a stabilizing complex compound of bivalent iron with a nitrogen-containing heterocyclic compound, which is free of mercaptoor thio-substituent groups, as ligand of a series selected from the group consisting of the pyrrole, pyrroline or pyrrolidine series, the imidazole, imidazoline or imidazolidine series of the pyridine series, the oxazole series,

-the oxazine series, the pyrazole, pyrazoline or pyrazolidine series.

2. The photographic material of claim 1, wherein the binding agent of the emulsion layer comprises a material selected from the group consisting of casein, albumine, starch or a starch derivative, cellulose or a cellulose derivative, alginic acid or an alginic acid derivative, polyvinyl ,pyrrolidine, polyvinyl-alcohol, partly hydrolyzed polyvinyl acetate or colloidal silica. 

2. The photographic material of claim 1, wherein the binding agent of the emulsion layer comprises a material selected from the group consisting of casein, albumine, starch or a starch derivative, cellulose or a cellulose derivative, alginic acid or an alginic acid derivative, polyvinyl pyrrolidine, polyvinyl-alcohol, partly hydrolyzed polyvinyl acetate or colloidal silica. 